Generally, such packs comprise a thin, planar plastic film formed in an envelope containing therein a liquid medium which is either cooled or warmed prior to application to the body. One of the disadvantages of such packs is that they do not readily conform to body contours, particularly around joint areas. The shaping forces tend to collapse the bags over a relatively wide area, so reducing the amount of liquid medium in those areas where it is most needed.
The liquid medium contained in reusable therapeutic packs, particularly where they are for use in cooling is normally water, together with a freezing point depressant such as propylene glycol or glycerol, whereby the liquid medium will be frozen to a slush of ice crystals at normal freezer temperatures, about 0.degree. F. Because of the low conformability of the planar film bags, relatively high concentrations of freezing point depressant are employed, so as to form only a thin slush of ice crystals. This increases the manufacturing cost of the packs, but more importantly, it reduces the heat capacity very significantly in comparison to a crushed ice pack, and it does not permit adequate treatment times with a single therapeutic pack of normal dimensions.